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ISU Extension Logo

Northwest Iowa Extension
Bean Leaf Beetle Management
by Todd Vagts
ISU Extension Crops Specialist
Counties Served:  Carroll, Calhoun, Crawford, Ida, Monona, Pocahontas and Sac.

Bean Leaf Beetle

   
 

 

1st Generation Bean Leaf Beetle Monitoring and Scouting procedures

Begin scouting first generation Bean Leaf Beetles one week after the predicted peak emergence of the 1st generation to determine control strategies for the 2nd generation (next month).  Peak 1st generation emergence will occur around 1212 GDD’s following soybean emergence.

ISU has developed a control strategy (for 2nd generation beetles in Mid-August and September) based on 1st generation population numbers. Based upon a high density of first generation beetles, it is expected that the second generation will exceed the economic threshold. This new management concept stops the second-generation beetles long before they reach the old economic threshold.

The first thing to do is determine the date soybeans emerged, then refer to the accumulated GDD graph and match dates. Begin sampling fields 1 week after peak emergence. If the sample is below threshold (Table 1), scout again the next week. If the sample is still below threshold, scout 1 more week. If 1st generation beetles are above threshold, scout again mid August to confirm beetles are present, then spray.

Notice: This is scouting of 1st generation beetles to determine control of 2nd generation beetles.

 

Figure 1.  Degree Day Accumulation for predicting emergence of 1st Generation BLB based on emergence date of the soybean field.

Degree-Day Data as of July 11, 2005


Figure 2.  Overwintered, First and Second generation bean leaf beetle estimated population cycle.

Bean leaf beetle generation cycles

 

Table 1. 1st generation economic thresholds necessary to spray 2nd generation beetles

 

treatment cost per acre (insecticide + application)

crop value ($/bushel)

$10.00

$12.00

$14.00

$10.00

$12.00

$14.00

 

beetles per 3 row feet

beetles per 20 sweeps

$5.00

7.9

9.5

11.0

32.6

39.0

45.4

$6.00

6.6 7.9 9.2 27.3 32.6 38

 

More information on this subject can be obtained from these url's

Management of second-generation bean leaf beetles (7/8/2002)
http://www.ipm.iastate.edu/ipm/icm/2002/7-8-2002/blbnextgen.html

Recent bean leaf beetle and bean pod mottle virus research (4/28/2003)
http://www.ipm.iastate.edu/ipm/icm/2003/4-28-2003/blbresearch.html

Bean leaf beetle identification (7/29/2002)
http://www.ipm.iastate.edu/ipm/icm/2002/7-29-2002/beenleafbeetleid.html

 

 


Todd Vagts
Iowa State University Extension
Field Crops Specialist
1240 D. Heires Avenue 
Carroll, IA 51401 
Office: 712-792-2364; Cell: 712-249-6025;  Fax: 712-792-2366
Email: vagts@iastate.edu  


For questions or comments please respond to vagts@iastate.edu

This page last updated on 07/18/05

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